Corrosion protection of metals



Patented Mar. 13, 1945 CORROSION PROTECTION OF METALS Emmett R. Barnum, Berkeley, and Ernest W.

Zublin, Sausalito, Califi, assignors to Shell Development Company, San Francisco, Call! a corporation of Delaware No Drawing. Application February 8, 1943, Serial No. 475,206

12 Claims.

The present invention relates to metals or metal-containing articles of manufacture which are normally subject to corrosion and which have been rendered substantially non-corrodible by treatment with a dispersion of a certain free dicarboxylic acid in a suitable vehicle.

Metallic surfaces, particularly those containing iron, require protection against the hazard of corrosion in the presence of water. To illustrate: Moisture readily attacks finished or semi-finished metal objects unless the metal surface is covered during storage or shipment'by a protective coating such as a slushing oil; water in Diesel engine fuels often corrodes closely fitted parts such as are found in Diesel engine unit type injectors; water in turbines corrodes turbine lubricant circulatory systems, particularly the governor mechanisms of steam turbines; and water in hydrocarbon oils such as gasoline rusts steel storage tanks and drums; water in anti-,freeze compositions causes corrosion in automobile radiators, etc. Corrosion not only has a deleterious effect upon the metal surfaces, but also frequently loosens finely divided metal oxides which may act as oxidation catalysts increasing the rate of deterioration of various organic compounds with which they come in contact or may enter between moving parts of machinery where they act as abrasives.

It is a purpose of this invention to treat metals or articles of manufacture containing metals in a way so that they become resistant to their normal corrosion. It is a specific purpose to treat in a simple manner accurately machined metal parts so that they may be handled without developing corrosion, particularly in places where fingerprints have been left. Another purpose is to protect iron or steel equipment exposed to the atmosphere so that its rusting is prevented or at least retarded. Still another purpose is to protect mechanical equipment from rusting, which equipment stands idle and/or is shipped over long distances.

We have discovered that structural metals which are used in the construction of various articles of manufacture and are subject to a normal corrosion can be protected simply and efiectively by treating them with a fine dispersion of a dicarboxylic. acid having at least 16 carbon atoms wherein the carboxyl radicals are linked by a carbon chain and wherein at least one ether type radical branches from this chain.

By ether type radical we mean a grouping wherein at least one atom of the elements 0, S, Se or Te is attached to two separate carbon atoms, such as in employed. The lower temperature limit is usually determined by the solidification temperature of.

the liquid, and temperatures should be below the boiling temperature of the vehicle and below the decomposition temperatures of both the vehicle and the dicarboxylic acid.

Metals capable of being thus protected are in particular the ferrou 'metals, e. g., soft iron, various steels, cast iron, and to a lesser extent copper, brass, bronze, zinc, aluminum, magnesium alloys, various bearing metals as copperlead, cadmium-nickel, silver-nickel, etc.

Articles containing these metals are too numerous to recite. However, it may be mentioned that the problem of rust prevention is critical, for example, where accurately machined parts are involved, such as piston rings, engine cylinders, bearing shafts, plungers of pumps, etc. In other instances, rust prevention may perhaps not be critical, but of vast economic importance as, for example, in the mass production of steel castings which are piled up and often set in the open for months before being finished.

oxygen, C02, salts, inorganic or organic acids, etc.

The treatment, according to this invention, for the prevention of corrosion may consist of a single contact of the metal to be protected with the dispersion containing the dicarboxylic acid, or may comprise repeated contacts effected at intervals, or may consist of a continuous treatment lasting as long as the use of the particular dispersion or piece of equipment or both. The choice of any particular type of these treatments is usually dictated by circumstances. For example, if newly machined and finished machine parts are to be rust-proofed, they may be clipped or sprayed with a suitable dispersion, and then stored away. On the other hand, if rust prevention in a steam turbine is desired, it is preferable that the circulating lubricating oil contain the active rust-preventive compound and contact is made as long as this oil is used. Should, after a while. this oil be discarded and be replaced by another one not containing a rust-preventive, then corrosion protection usually lasts for a long time thereafter, due to the protective film left behind. In cases where this film is mechanically destroyed, as in bearings or gears, etc., running under extreme loads, the protective film must be renewed continuously; otherwise rust protection fails.

The general formula of the crrosi0n-preventive acids of this invention is:

coon (a-x cna.)). -c-);

wherein u is an integer from 1 up to about 8 and preferably 2, v is an integer from zero up to about 8, preferably zero, w is at least 1, preferably 1 or 2, and never greater than u, X is an element of the class 0, 8, Se or Te, and R is a hydrocarbon radical. Unoccupied valences may be tied to the same or different hydrogen or hydrocarbon radicals.

The several hydrocarbon radicals may be allphatic, alicyclic, aromatic or mixed and may contain substituents which are preferably not too strongly polar, such as halogen, but are preferably free from highly polar substituents, such as hydr'oxyl, carboxyl, carbonyl, amino, hydrosulfide, etc. For maximum stability against deterioration by oxidation, the acid should contain not more than one aliphatic double bond per hydrocarbon radical, and preferably none.

As indicated above, the acid should contain not less than 16, and preferably at least 20 and up to 60, carbon atoms for good anti-corrosion proper ties. Also, the closeness of the O, S, Se or Te, as the case may be, to the carboxyl radicals has a bearing on this property, in general the closer they are, the greater the protective power. Because of this, homologues in which the ether linkage is in alpha or beta position to at least one and preferably both carboxyl radicals are most desirable.

The simplest of these acids are the malonic acid derivatives illustrated'below:

coon

a-x-c coon coon

R-X-CHr-C coon wherein again X is 0, 8, Be or Te and R is a hydrocarbon radical. However, this type of acid is thermally quite unstable, easily losing C01. Therefore, for many purposes it is not desirable. Succinic or fumaric (maleic) acid ether type derivatives, of which there are several, are very stable. They are:

HOOC- BR Any of these is very effective.

There are many derivatives of glutonic acid, a few of which are shown below:

RX-CH-COOH Eli-coon car-coon RX- n m-coon ax-cn-coon ax-cn-coon ax-eB-coon 40 From the above it can be readily seen what may form the linkage.

forms the dicarboxylic acid ethers may take, in which acids the carboxyl radicals are separated by four and more carbon atoms.

Where X stands for sulfur, two sulfur atoms In other words, com pounds of the following types are included in this invention:

RSS-CH-COOH H-COOH RSB-CH-COOH RBS- H-COOH As'may be noted, there are two general groups of dicarboxylic acids among those listed above, those containing a single ether type radical and those containing two ether type radicals. Under many circumstances, the acids containing two ether type radicals are preferred because they have the ability of giving material corrosion protection in stagnant salt water. A form of corrosion which is probably most difficult to inhibit is that caused by a drop of salt water resting undisturbed on ametal surface. Few, if any, corrosion inhibitors which are not of the soap type are capable of effectively preventing this corrosion. However, the bis-ether type acids and particularly the his sulfides of this invention have been proven to prevent corrosion against stagnant salt water for several days.

The compounds of this invention are quite soluble in many organic solvents. Wherever possible, true solutions are employed in preference to colloidal solutions for two reasons: first,

, producthas the required minimum of 16 carbon atoms. This hydrocarbon radical may be normal and/or cyclic, examples being heptyl, methyl cyclohexyl, normal or branched octyl, dimethyl cyclohexyl, ethyl cyclohexyl, nonyl, decyl, undecyl, dodecyl, lauryl, myristyl, cetyl,

stearyl, oleyl, arachyl, benzyl, methyl phenyl,.

ethyl phenyl, dimethyl phenyl, propyl phenyl, butyl phenyl, octyl phenyl, naphthyl, alkyl naphthyl, tetrahydronaphthyl, C and higher dialicyclic, etc.

The vehicles to which dicarboxylic acids of this invention may be added for the purpose of producing corrosion-protective compositions may be divided into several groups.

For example,

In the first place,

stearates, oleates, ricinoleates, phthalates, ads-ii,

phates, phosphites, thio-phosphates, carbonates;

natural waxes as camauba wax, candelllla wax.

- Japan wax, jojoba oil, sperm oil; fats as tallow,

they may be liquids or plastics, the only requirements as to their physical state being (in addition to their being able to act as carrier for the acids under normal atmospheric conditions) that they be spreadable over metal surfaces. Spreading may be accomplished by immersing, flooding, spraying, brushing, trowelling, etc.

After being applied, all or part of the vehicle may be evaporated, or it may be more or less permanent. In other words, both volatile carriers may be used, or substances which do not materially volatilize under normal atmospheric conditions. As to chemical requirements, the vehicle must be stable under ordinary conditions of storage and use and be inert to the active inhibitors.

Thus the vehicle should preferably be substantially neutral, although it may be weakly acidic or basic, preferably having dissociation constants not above about 10 In vehicles of low dielectric constant, as hydrocarbon oils, which are not conducive to ionization of dissolved electrolytes, relatively small amounts, i. e., about .1 %-5% of various carboxylic acids, such as fatty or naphthenic acids, may be present, and in many instances this may even be beneficial.

Both polar and non-polar vehicles may be employed. Among the former are water, alcohols, such as methyl, ethyl, propyl, isopropyl, butyl, amyl, hexyl, cyclohexyl, heptyl, methyl cyclohexyl, octyl, decyl, lauryl, myristyl, cetyl, stearyl, benzyl, etc., alcohols; polyhydric alcohols as ethylene glycol, propylene glycol, butylene glycol, glycerol, methyl glycerol, etc.; phenol and various alkyl phenols; ketones as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl, methyl butyl,, dipropyl ketones, cyclohexanone and higher ketones; keto alcohols as benzoin, ethers as diethyl ether, dilsopropyl ether, .diethylene dioxide, beta-beta dichlor diethyl ether, diphenyl oxide, chlorinated diphenyl oxide, diethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, corresponding ethyl,'propyl, butyl ethers; neutral esters of carboxylic and other acids as .ethyl, propyl, butyl, amyl, phenyl, cresyl and higher acetates, propionates, butyrates, lactates, laurates, myristates, palmitatcs,

lard oil, olive oil, cottonseed oil, perilla oih'lin t seed oil, tung oil, soya bean oil, flaxseed'oilfetcq weak bases as pyridine, alkyl nolines,petroleum bases, etc.

Vehicles of little or no polarity comprise. drocarbons or halogenated hydrocarbons,a.s -liq-- uid butanes, pentanes, hexanes, heptanesfQ oc-g; tanes, benzene, toluene, xylenes, cumene,iindene,lv

hydrindene, allgvl naphthalenes; gasoline. distillates, kerosene, gas oil, lubricating oils; (which may be soap-thickened to formgreases), petro laturn, paraflin wax, albino asphalt, carbon tetra, U

chloride, ethylene dichloride, propylchloride,

butyl chloride, chlorbenzol, chlorinatedlgerosene,

chlorinated paraflin wax, etc.

The amounts of the dicarboxylic must be incorporated in the above vehiclestoproduce corrosion-protective compositions y'va y considerably with the type of vehicle used As general rule, the presence of resinous materials,: f:

particularly those of a colloidal nature calls for relativelylarger amounts of inhibitorsn resins, various other natural resins, as rosin, resins formed by polymerization of drying fatty oils, phenolformaldehyde resins, 'glyptal type resins formed by esterification of polyhydric alcohols with polycarboxylic acids, etc.

about .1% may resultin relativelyquiclg-loss of part of the inhibitor by precipitation and settling, In the presence of resins and otherycolloidspn amounts in excess of .l% and upto 5%maybe required. Inasmuch as resins may act as protective colloids, compositions containing these large amounts of colloidally dispersed inhibitors, together with resin, may be quite resistant to precipitationand settling. I

Since resinous and gummy substances-gimme, vehicles do call for greater amounts of inhibitors,. it is usually desirableto refine normally liquidwv vehicles thoroughly and free them from gummy substances, thereby imparting to them maxi-.13.; mum inhibitor susceptibility. This is of ;.1par. ticular importance, for example, in lubricating-w oils, specifically steam turbine oils, which are advantageously highly refined'before the inhibitor is introduced. Suitable refining treatments include, for example, extraction with selective solvent for aromatic hydrocarbons as liquid S02,

phenol, furfural, nitrobenzene, aniline, beta-betadichlor diethyl ether,'antimony trichloride, etc.; treatment with AlCls, sulfuric acid, clay, etc.; as the treatment produces a sludge, special care must be taken to remove it very thoroughly and completely.

Example py ne- .qu e.

bye...

i it, ous materials which interfere with the act vitypf the inhibitors comprise asphaltenes, petroleum,

volume sea water at 187 1". Below are some typical results:

Mter the test was completed, stirring was discontinued and the steel strip was allowed to drop into the sea water at the bottom the container, remaining there undisturbed for four days. At the end of this period, only a few small rust spots had developed.

We claim as our invention:

1. A structural normally corrodible metal coated with a corrosion-preventive film of a free dicarboxylic acid having at least 16 carbon atoms and possessing at least one ether type radical of an element selected from the group consisting of O, S, Se and Te, which ether type radical branches from the carbon chain linking the carboxyl radical.

2. The coated material of claim 1, the film of which contains an acid having between 20 and 60 carbon atoms.

3. A structural normally corrodible metal coated with a corrosion-preventive film of a free dicarboxylic acid having at least 16 carbon atoms and having the formula wherein u is an integerof 1 up to about 8, o is an integer of from 0 to about 8, w is at least 1 and not greater than u, X is an element selected from the group consisting of 0, S, Se and Te, and R is hydrocarbon radical, and the unoccupied valences are tied to hydrogen or hydrocarbon radicals.

f1. A structural normally corrodible metal coated with a corrosion-preventive film. of a free dicarboxylic acid having at least 16 carbon atoms and having the formula wherein X is an element selected from the group consisting of O, S, Se and Te, R1 and R2 are hydrocarbon radicals and the unoccupied valences are tied to hydrogen or hydrocarbon radicals.

5. A structural normally corrodible metal coupled with a corrosion-preventive him of a free dicarboxylic acid having at least 16 carbon atoms and having the formua wherein X is an element selected from the group consisting of O, 8, Se and Te and R is a hydrocarbon radical.

6. A structural normally corrodible metal coated with a corrosion-preventive film of a succinic acid ether having at least 16 carbon atoms.

"1. A structural normally corrodible metal coated with a corrosion-preventive film of a succinic acid thio ether having at least 16 carbon atoms.

8. A structural normally corrodible metal coated with a corrosion-preventive film of a succinic acid di thio ether having at least 16 carbon atoms.

9. A ferrous metal coated with a rust-preventive film of a free dicarboxylic acid having at least 16 carbon atoms and possessing at least one ether-type radical of an element selected from the group consisting or 0, 8, Se and Te, which ether-type radical branches from the carbon chain linking the carboxyl radicals.

10. An article of manufacture comprising a structural normally corrodible metal treated with a fine dispersion in a substantially neutral vehicle of a dicarboxylic acid having at least 16 carbon atoms and possessing at least one ether-type radical of an element selected from the group consisting of O, S, Se and Te, which ether-type radical branches from the carbon chain linking the carboxyl radicals.

11. Method of protecting a normally corrodible structural metal from corrosion comprising spreading over its surface a fine dispersion in a substantially neutral vehicle of a dicarboxylic acid having at least 16 carbon atoms to deposit on said metal a protective coating of said acid, said acid possessing at least one ether-type radical of an element selected from the group consisting of O, S, Se and Te, which ether-type radical branches from the carbon chain linking the carboxyl radicals.

12. Method of protecting a normally corrodible structural metal from corrosion comprising spreading over its surface a fine dispersion in a substantially neutral vehicle of a dicarboxylic acid having at least 16 carbon atoms and having the formula ax-cm-coon wherein X is an element selected from the group consisting of O, S, Se and Te, and R is a hydrocarbon radical.

ERNEST W. ZUBLIN. EMME'II R. BARNUM. 

